The invention relates to a GPRS type of packet radio network and more specifically to reduction of signaling load therein as a mobile station changes routing areas.
A General Packet Radio Service (GPRS) is a new service in the GSM. It is one of the items that are being standardized in GSM (Global System for Mobile Communication) phase 2+ at the ETSI (European Telecommunication Standard Institute). The GPRS operational environment consists of one or more sub-network service areas that are interconnected by a GPRS backbone network. A sub-network comprises a number of packet data service nodes, which are herein called GPRS support nodes (or agents) and each one of which is connected to the GSM mobile network so that it can provide packet data service for mobile data terminals via several base stations, i.e. cells. An intermediate mobile network provides circuit-switched or packet-switched data transmission between a support node and the mobile data terminals. Different sub-networks, in turn, are connected to an external data network, for example to a Public Switched Packet Data Network (PSPDN). The GPRS service can thus be used for effecting packet data transmission between mobile data terminals and external data networks, with the GSM network functioning as an access network. One of the features of the GPRS service network is that it operates almost independently. of the GSM network. One of the requirements set for the GPRS service is that it must operate together with different types of external PSPDN networks, such as the Internet and X.25 networks. In other words, the GPRS service and the GSM network should be able to serve all users, irrespective of the type of data networks that they wish to be connected to via the GSM network. This means that the GSM network and GPRS service must support and process different network addressing methods and data packet formats. The data packet processing also comprises routing of packets in a packet radio network. In addition, users should be able to roam from their home GPRS network to a visited GPRS network.
FIG. 1A illustrates a typical arrangement in a GPRS network. The architecture of GPRS networks is not as mature as that of the GSM networks. All GPRS terms should therefore be understood as being descriptive rather than limiting. A typical mobile station forming a mobile data terminal consists of a mobile station MS in a mobile network and of a portable computer PC connected to the data interface of the MS. The mobile station may be, for example Nokia 2110, manufactured by Nokia Mobile Phones Ltd., Finland. By means of a PCMCIA type Nokia Cellular Datacard, manufactured by Nokia Mobile Phones Ltd., the mobile station can be connected to any portable personal computer PC that has a PCMCIA card slot. The PCMCIA card thus provides the PC with an access point that supports the protocol of the telecommunication application used in the PC, such as the CCITT X.25 or Internet Protocol IP. Alternatively, the mobile station can directly provide an access point that supports the protocol used by the PC application. Further, a mobile station 3 and a PC 4 can be integrated to form a single unit, within which the application is provided with an access point that supports the protocol used by it. An example of such a mobile station with an integrated computer is a Nokia Communicator 9000, manufactured by Nokia Mobile Phones Ltd., Finland.
Network elements BSC and MSC are previously known from a typical GSM network. The arrangement of FIG. 1A comprises a separate Serving GPRS Support Node (SGSN). The support node controls certain operations of the packet radio service on the network side. The operations include logging on and off the system by the mobile stations MS, routing area updates by mobile stations MS, and data packet routing to correct destinations. In the present application, the term xe2x80x98dataxe2x80x99 should be understood in the wide sense to refer to any information transmitted to/from a terminal in a digital telecommunication system. The information can comprise speech encoded into digital form, data communication between computers, telefax data, short segments of program code, etc. Information outside data transmission, such as subscriber data and related inquiries, routing area updates etc., is called signaling. The SGSN node can be located at a base station BTS, at a base station controller BSC or at a mobile switching center MSC, or it can be separate from all these elements. The interface between the SGSN node and the base station controller BSC is called a GB interface. An area managed by one base station controller BSC is called a Base Station Subsystem BSS.
The intermediate mobile network provides packet-switched data transmission between a support node and mobile data terminal equipment. Different sub-networks, in turn, are connected to an external data network, for example to a PSPDN, via a specific GPRS gateway support node GGSN. Packet data transmission between mobile data terminals and external data network functioning as an access network. Alternatively, the gateway node GGSN can be replaced with a router. In the following, the term xe2x80x98gateway node GGSNxe2x80x99 is also to be understood to refer to a structure in which the gateway has been replaced with a router.
In FIG. 1A the GPRS network connected to the GSM network comprises a number of serving GPRS support nodes SGSN and one gateway GPRS support node GGSN. The different support nodes SGSN and GGSN are interconnected via an intra-operator backbone network. It is to be understood that a GPRS network may comprise any number of support nodes SGSN and gateway nodes GGSN.
Each support node SGSN manages a packet data service in the area of one or more nodes in a cellular packet radio network. To achieve this, each support node SGSN is connected to a certain local part of the GSM system, typically to a mobile services switching center, but in some situations it may be preferable to connect it directly to a base station subsystem BSS, i.e. to a base station controller BSC or a base station BTS. A mobile station MS in a cell communicates with a base station BTS over a radio interface and further through a mobile network with the support node SGSN to the service area of which the cell belongs. In principle, the mobile network between the support node SGSN and the mobile station MS only transmits packets between these two. For this purpose, the mobile network can offer either a circuit-switched connection or packet-switched data packet transmission between a mobile station MS and a serving support node SGSN. An example of a circuit-switched connection between a mobile station MS and an agent is presented in FI 934115. An example of packet-switched data transmission between a mobile station MS and an agent is presented in FI940314. It should be noted, however, that a mobile network provides only a physical connection between a mobile station MS and a support node SGSN, and that its exact operation and structure are not relevant to the invention.
An intra-operator backbone network 11 interconnecting an operator""s SGSN and GGSN can be implemented by a local area network, for example. It should be noted that an operator""s GPRS network can also be implemented without an intra-operator backbone network, by implementing all features in a single computer, for example, but this does not cause any changes in the call set-up principles according to the present invention.
A GPRS gateway node GGSN connects an operator""s GPRS network to other operator""s GPRS networks and to data networks, such as an inter-operator backbone network 12 or an IP network. An Interworking Function IWF can be arranged between the gateway node GGSN and the other networks, but usually the GGSN is simultaneously the IWF. The inter-operator backbone network 12 is one through which the gateway nodes GGSN of different operators can communicate with one another. The communication is needed to support GPRS roaming between the different GPRS networks.
The gateway node GGSN is also used for storing the location information of the GPRS mobile stations. The GGSN also routes mobile-terminated (MT) data packets. The GGSN also contains a database that associates the mobile station""s network address in an IP network or an X.25 network (or simultaneously in more than one network) with the mobile station identifier in a GPRS network. When the mobile station roams from one cell to another within the area of one support node SGSN, a routing area update is needed only in the support node SGSN, and the gateway node GGSN need not be informed of the change of routing area. When the mobile station roams from a cell of one support node SGSN to a cell of another SGSN within the area of the same or a different operator, an update is also performed in the (home) gateway node GGSN so as to store the identifier of the new, visited support node and the identifier of the mobile station.
A home location register HLR is also used to authenticate subscribers at the beginning of a GPRS session. It contains a definition between a subscriber""s PDP (Packet Data Protocol) address (addresses) and the subscriber""s IMSI (International Mobile Subscriber Identity). In a GSM network a subscriber is identified on the basis of the IMSI. In FIG. 1A the HLR is connected through SS7 (Signaling System 7), for example to a mobile switching center MSC and an intra-operator backbone network. Between the SS7 signaling system and the intra-operator backbone network there can be a direct connection or an SS7 gateway node. In principle, the HLR can exchange packet-switched messages with any GPRS node. The HLR""s method of communication and its connection to the GPRS network are not, however, essential to the invention.
When packet data is sent to a mobile station, the data will be routed to the correct GSM network via the gateway node GGSN to the support node SGSN in which the location of the mobile station is known. If the mobile station is in standby mode, its location is known with the accuracy of a Routing Area (RA). Correspondingly, if the mobile station is in ready mode, its location is known with the accuracy of a cell.
FIG. 1B shows signaling associated with routing area maintenance. For the sake of clarity, FIG. 1B is highly simplified and only shows the most essential messages. Resource reservations and releases, for example, known by a person skilled in the art, are not shown.
In step 1-1 a mobile station MS registers in the network and sends to the network a Routing Area Update message, which is relayed to a node SGSN1. In step 1-2 the SGSN, relays the message to the home location register HLR. In steps 1-3 and 1-4 corresponding acknowledgements are sent to the node SGSN, and to the mobile station MS. At the horizontal broken line in FIG. 1B, the mobile- station MS moves from the area of the node SGSN, to the area of a node SGSN2. Steps 1-5 to 1-8 correspond to steps 1-1 to 1-4 except that this time the routing area update message passes via the node SGSN2. In addition, in step 1-9 the home location register HLR sends a routing area cancellation to the node SGSN, which deletes the data on the mobile station MS from its register. The assumption in FIG. 1B is that the mobile station MS roams within the area of its home network. Should the mobile station MS roam in a visited network (e.g. network 1), the routing area update should be routed further via the gateway nodes GGSN to the home network (similarly to network 2).
A problem in the above prior art arrangement is the great signaling load generated on the one hand between the support node SGSN and the gateway node GGSN and on the other hand between the support node SGSN and the home location register HLR. Particularly much signaling load is generated when the support node SGSN has a small service area. In that case a roaming mobile station causes much signaling in the network (routing area updates). Every time a mobile station MS moves from the area of an old support node (e.g. SGSN1) to the area of a new support node (e.g. SGSN2), it sends a routing area update message to the network. This generates signaling between the gateway node GGSN and both support nodes SGSN. The problem is at its worst when the mobile station roams within the area of another network than its home network, since information on a change in routing areas has to be relayed all the way to the home network of the mobile station.
Furthermore, prior art GPRS recommendations suggest that information on the location of a mobile station MS always be maintained in the network home location register HLR. It is obvious that continuous updating of the location of all mobile stations in the network in one network element (home location register) causes unreasonable load to said network element.
It is thus an object of the invention to provide a method and an apparatus for implementing the method so as to solve the above problems related to heavy signaling load and the load on the home location register HLR. The objects of the invention are achieved by a method and an arrangement, characterized by what is disclosed in the independent claims. The preferred embodiments of the invention are disclosed in the dependent claims.
The invention is first of all based on the observation that an SGSN node capable of dealing with a large number of messages within an extensive area is difficult to implement by conventional technology. In other words, conventional technology provides poor scalability for an SGSN node.
The invention is also based on complementing the functionality of the support node SGSN in the following manner. A support node according to a preferred embodiment of the invention has a plurality of IP addresses intended for data transmission and to deal with given routing areas. A support node of the invention needs (as does a conventional support node) only one SS7 address and one control IP address (hereinafter also IP1). Internal control functions of a support node of the invention manage the mobility of mobile stations and maintain information on which data transmission IP address is serving each mobile station at each particular time. Information on a change in IP addresses within the area of the same support node is relayed to the gateway node GGSN, but not to the home location register HLR. Information on the movement of a mobile station is relayed to the home location register only in case the support node serving the mobile station changes.
One application of the invention is such that data transmission IP addresses handle a given number of active connections but are not tied to a given area. In this case location update is not even needed to the gateway node in updating an internal routing area of the support node. The structure of the support node and the distribution of tasks between different parts remain otherwise the same in this interpretation.
An advantage of the invention is significant reduction in signaling need and the load on the home location register HLR. Another advantage is that a support node can be scaled very well, i.e. its capacity can be increased flexibly by increasing blocks, or modules, serving data transmission. A dedicated IP address (hereinafter also IP2, IP2xe2x80x2, IP2xe2x80x3 etc.) for data transmission is given to each data transmission module. Good scalability again provides the advantage that network planning becomes flexible since with increasing traffic the network architecture does not have to be changed (e.g. to increase support nodes), but the capacity of existing support nodes can be increased flexibly.
Some advantages of the invention, such as good scalability, are achieved simply by modular implementation of a support node. In other words, the parts serving data transmission constitute a separate module and the support node comprises already upon installation the mechanical, electrical and software facilities for multiple module installation. The changes needed in other network elements are minimal or no changes are needed at all.